This invention relates to mechanical brake units for cargo dollies like those used by airport ground services to transport unit load devices, cargo pallets, and baggage.
Cargo dollies stop by actuating a mechanical brake unit that is connected by a tie rod to the tow bar. The brake, which is positioned just ahead of the rear tires (toward the forward end of the dolly), automatically pushes against and locks the rear tires when the tow bar is in a vertical position and pulls away from and releases the tires when the tow bar is in a horizontal position (see e.g. U.S. Pat. No. 8,851,488 B2 at FIG. 4). A compression spring that surrounds tie rod keeps the left and right brake pad weldments pressing against the tires. The spring does not store energy during the braking process. Alternatively, or in addition to the spring, the tie rod includes an adjustment weldment. However, each style of brake loses its effectiveness as the rear tires wear.
Tire wear can be substantial. It is not uncommon for the tires to remain in service until about a ½ inch of tread wear occurs (taking a 4.00×8 solid tire down to about 14¾ to 15-inches in diameter). Even more troublesome, the wear oftentimes is uneven within and between each left and right pair of tires.
Because the dollies can hold up to 15,000 pounds, and are used on inclines and around people and expensive equipment, braking effectiveness and reliability is a critical safety and cost issue. Therefore, a need exists for an improved rear brake unit.